Injection Device, in Particular For Injecting a Hydrocarbon Feedstock into a Refining Unit

ABSTRACT

Embodiments of the invention relate to an injection device configured to atomize a liquid into droplets using a gas, comprising a body comprising walls defining a recess, a liquid inlet orifice being formed laterally in said walls, and a gas injection assembly in which there is formed a passage for the circulation of gas between a gas inlet orifice at one end of the recess and a gas outlet orifice situated inside the recess, this assembly defining, with the walls of the body, a space for the circulation of liquid from the liquid inlet orifice to the constriction, and wherein the walls of the body define a constriction having a throat, downstream of the gas outlet orifice, and the injection device is arranged in such a way that the stream of gas at the outlet orifice covers a wall portion in close proximity to the throat.

The present invention relates to an injection device, notably to adevice for injecting a charge of hydrocarbons for a refinery unit,particularly a fluid catalytic cracking (FCC) unit.

The charges of liquid hydrocarbons processed in refinery units aregenerally brought into contact with a solid catalyst which willencourage the chemical reaction or reactions for processing the charge.In order to improve this contact and maximize the yield of thereactions, these liquid hydrocarbon charges are atomized into finedroplets by injecting devices. This atomization makes it possible tomaximize the area for contact between liquid (liquid hydrocarbon charge)and solid (catalyst), thereby encouraging the transfer of heat andcontributing to the uniform distribution of the hydrocarbons within thereaction zone. Although there is no real consensus regarding the optimumdiameter of the droplets, the general aim is to form droplets thediameter of which is of the same order of magnitude as the diameter ofparticles of catalyst, namely under 200 microns, for example of theorder of 50 to 80 microns.

In general, use is made of injection devices referred to as “disphasic”which have a hollow cylindrical body and two inlet openings via whichthe liquid hydrocarbon charge on the one hand, and an atomizing gas,generally steam, on the other hand, are injected into said body. Acontact chamber is formed inside the body, and this is where thehydrocarbons, and the atomizing gas are brought into contact in order toatomize the charge of hydrocarbon. Once atomized, the hydrocarbon chargeis ejected via an outlet opening that opens into the inside of thereactor.

Each injection device is installed on a reactor wall such that one endof the injection device comprising the outlet opening is situated on theinside of the reactor.

Venturi-type injection devices in which the charge is propelled througha Venturi in combination with an atomizing gas leading to the formationof droplets are notably known. Said atomization gas flowing axiallyallows these droplets to be carried along, dividing them further towardsthe outlet of the body.

There is a need for an injection device that is able to combinesimplicity with low pressure drop and high quality atomization.

There is provided an injection device configured to atomize a liquidinto droplets using a gas, comprising:

-   -   a body comprising walls defining a recess extending axially so        that it opens on the one hand towards a gas inlet orifice at one        end of the injection device and, on the other hand, towards an        atomized-liquid outlet orifice at the other end of the injection        device, and a liquid inlet orifice being formed in these walls,        this liquid inlet orifice extending along a radial component so        as to open, on the one hand, to the outside of the body and, on        the other hand, onto the recess,    -   a gas injection assembly in which there is defined a passage for        the circulation of gas between the gas inlet orifice and a gas        outlet orifice situated inside the recess,

wherein

-   -   the walls of the body define a constriction the throat of which        is downstream of the gas outlet orifice,    -   the gas injection assembly defines, with the walls, a space for        the circulation of liquid from the liquid inlet orifice towards        the throat of the constriction, and    -   the injection device is arranged in such a way that the stream        of gas emanating from the gas outlet orifice covers a wall        portion in close proximity to the throat of the constriction.

It has been found that by combining a constriction throat with a streamof gas over or very close to this throat, it was possible to obtain arelatively good atomization in terms of droplet diameter, and to do sowith a relatively low pressure drop. It is possible that the liquid filmpassing near the throat of the constriction is sheared by the jet of gasfrom the gas injection assembly, thus causing the liquid to be atomizedinto droplets.

The wall portion in close proximity to the throat may include:

-   -   a wall portion upstream of the throat, extending as far as the        throat or not, and/or    -   a wall portion downstream of the throat, extending as far as the        throat or not.

“In close proximity to the throat” means very small distances away fromthe throat, for example distances of less than 5% of the maximumdiameter of the body, advantageously of less than 1% of this diameter,possibly of less than 0.1% of this diameter.

Advantageously, the throat may be contained in the wall portion coveredby the stream of gas.

A “constriction” means a throttling down of the cross section of therecess as far as a throat. Downstream of the throat, the cross sectionmay remain constant at the minimum diameter (at least locally) reachedat the throat, or increase again.

The “constriction throat” means a minimum, in terms of distance betweenthe wall and a central axis of the body, of the constriction. Stateddifferently, the throat constitutes one end of the constriction.

At the constriction, the walls may extend with a radial component as faras the throat. For a throat circumscribed in a plane normal to the axialdirection, the diameter of the cross section of the recess may thusreach a minimum at the throat.

The diameter of the cross section of the recess downstream of the throatmay remain identical or substantially identical to the minimum valuereached at the throat. Thus a portion referred to as a cylindricalportion may be provided downstream of the throat and extending as far asthe throat, in which portion a duct of cylindrical shape is formed.

In that case, the cylindrical duct may advantageously extend axiallyover a length of a magnitude at least four times, advantageously atleast five times, higher than the magnitude of a diameter of the crosssection of this duct. Surprisingly, this arrangement appears to make itpossible to obtain enhanced performance.

Alternatively, the diameter of the cross section of the recessdownstream of the throat may be higher than at the throat. The walls atthe constriction may for example define a bulge extending in a radialcomponent as far as the throat.

The throat may define a sharp-edged line, which means to say that thederivative, with respect to the axial position, of the distance betweenthe centred axial line of the body and the internal walls of the body isdiscontinuous at the throat.

Alternatively, the walls may be configured so that this derivativeremains continuous. The walls may for example define a constriction witha relatively rounded end edge.

The throat may be closed, for example the throat may have a circular orelliptical shape.

For example, a sharp-edged line may be circumscribed in a plane, or maynot be. When the sharp-edged line is in a plane, this plane may benormal to the axis of the body, or may not be. For example, it may bepossible to provide for the sharp-edged line to lie in a plane that isinclined with respect to the axis of the body.

Alternatively, the throat may be open. For example, the throat maydefine a non-closed line extending in a helix inside the body and havingone or more turns. Provision may also be made for there to be a set ofnon-closed lines extending in a helix and having one or more turns.

In an embodiment, the throat may define a segment, for example asharp-edged line, extending transversally and in a rectilinear way.

The body may be produced in one or several parts.

At the liquid may essentially contain a charge of hydrocarbons, orother.

The gas may essentially comprise steam, or other.

At the constriction, the cross section of the recess is smaller than ina portion of the body immediately upstream of the constriction.

The cross section of the recess upstream of the throat may varycontinuously as far as the throat. For example, walls forming a portionof a spherical surface or a portion of a conical surface may be planned.The constriction may, for example, define a volume representing aportion of a hyperboloid, a portion of a sphere or a portion of a cone,upstream of a sharp-edged line or of a rounded end.

Alternatively, the cross section of the recess upstream of the throatmay exhibit discontinuities. For example, a body the walls of which havea rib with no fillet where the base of the rib and the, for examplecylindrical, walls of the body meet may be provided.

In one advantageous embodiment, the gas outlet orifice is a slot facingthe throat so that the stream of gas is circumscribed in close proximityto the throat. This arrangement may make it possible to limit thequantity of gas injected into the injection device.

The slot may have a shape similar to the shape defined by the throat,for example a circular shape in the case of a circular throat, or arectilinear shape for a throat defining a segment extendingtransversally.

The slot width may thus be relatively small, for example less than 5% ofthe maximum diameter of the body, advantageously less than 1% of thisdiameter, possibly less than 0.1% of this diameter. The width of theslot may for example vary between 0.1 millimetres and 10 millimetres,advantageously between 0.5 millimetres and 5 millimetres, advantageouslybetween 1 and 2 millimetres.

The invention is by no means limited to gas outlet orifices formingslots. There may be provided several orifices having each one a verysmall size, with for example circular sections, each of said orificesbeing oriented such that the stream of gas from said orifice ends in (orpasses by) a close proximity of the throat.

Advantageously, the gas injection assembly may comprise a tube and a rodelement housed in said tube, this rod element extending longitudinallyinside the tube so that the passage for the circulation of gas isbetween said rod element and said tube. Such a principle of concentricdouble walls is used to create a passage and a gas outlet orifice thatform a slot of relatively small thickness.

The invention is by no means limited to such use of the principle ofconcentric double walls, even if it is advantageous because it isrelatively easy to manufacture. For example, there may be provided aconduit, the section of which changes along the passage for thecirculating of the gas, from a circular section near the gas inletorifice to a section having for example a shape of slot, for examplecircular or rectilinear. Alternatively, the gas injection assembly maydefine branch lines, such that the gas from the gas inlet orificedivides between several ducts of the capillary type, each of said ductsending near the throat.

Advantageously, at least one of the rod element and the tube can beconfigured so that the thickness of the passage for the circulation ofgas undergoes throttling that accelerates the velocity of the gasbetween the gas inlet and the gas outlet. The thickness of the passagemay thus be higher upstream of the gas outlet orifice than at thisorifice, for example between 5 millimetres and 5 centimetres, forexample of the order of 1 centimetre.

Advantageously, the rod element and the tube may be centred relative toone another so that a radial cross section of the rod and tube assemblyshows a constant distance between the surface of the rod and theinterior surface of the tube, whatever the radius considered.

Advantageously, the recess may be slightly flared downstream of theconstriction so that the diameter of the cross section of the recessincreases very slightly, over this portion of the recess thatcorresponds to the flared portion, as the distance from the throatgradually increases. For example, an angle of between 1° and 5° withrespect to the axial direction, advantageously of 3.5°, may be planned.Surprisingly, it would appears that this geometry makes it possible tolimit boundary layer separation.

An “axial line” means a line running parallel to the axial direction ofthe body of the injection device.

The invention also relates to a reactor for treating a charge ofhydrocarbons, notably for catalytic cracking, comprising at least oneinjection device as described hereinabove arranged in such a way thatits outlet orifice for atomized liquid opens inside the reactor.

The invention further relates to a method for the catalytic cracking ofa charge of hydrocarbons in a reactor, in which method the charge ofhydrocarbons is injected, preferably continuously, into this reactor,this charge of hydrocarbons being injected via a liquid inlet ductconnected to a liquid inlet orifice of an injection device as describedhereinabove, a gas simultaneously being fed into the injection devicevia the gas inlet orifice.

The charge of hydrocarbons may be injected in the liquid state, at atemperature ranging from ambient temperature to 500° C., for examplefrom 80° C. to 300° C., but more generally from 200 to 300° C. Thecharge of hydrocarbon may be injected at a pressure of the order of 6 to8 bar. More generally, the difference between the charge inlet pressureand the pressure at the injector outlet (delta P) may be comprisedbetween 0.8 and 5 bar.

The gas used may be steam or any other suitable gas, such as, forexample, a gaseous effluent resulting from the conversion ofhydrocarbons, light olefins or a mixture of these gases, a refinery gasor nitrogen.

Advantageously, in each injection device the proportion of gas withrespect to the charge of hydrocarbons is from 1.5 to 10 wt %, forexample from 2 to 5 wt %.

The flow rate in terms of the charge of hydrocarbons fed to eachinjection device may advantageously be controlled so as to obtain aspecific flow rate of hydrocarbon charge at the throat ranging from 1000to 2000 kg/m²/s, preferably from 1400 to 1800 kg/m²/s. This control maybe obtained in the conventional way by means of pumps, flow meters orthe like.

The velocity of the charge of hydrocarbon at the zone of contact withthe gas may be from 0.4 to 0.6 m/s, for example 0.5 m/s.

The velocity of the gas entering the zone of contact with thehydrocarbon may be from 100 to 200 m/s, for example 150 m/s.

The invention is now described with reference to the attachednonlimiting drawings, wherein:

FIG. 1 is a perspective view of one example of an injection deviceaccording to one embodiment of the invention;

FIG. 2A is a view from above of the example of the injection device ofFIG. 1,

FIGS. 2B and 2C are, respectively, views in cross section on A-A and B-Bof FIG. 2A, of the example of the injection device of FIGS. 1 and 2A;

FIG. 3 depicts the distribution of mean droplet size as a function ofspray width at a relative distance from the outlet orifice for anexample of an injector according to one embodiment of the invention andfor a reference injector comprising a Venturi;

FIG. 4 is a perspective view of a component of the example of aninjection device of FIGS. 1, 2A, 2B, 2C, namely a second gas supplyelement; and

FIG. 5 very schematically depicts an example of an injection deviceaccording to one embodiment of the invention.

Substantially parallel or perpendicular means a direction that divergesby at most ±20°, or even by at most 10° or by at most 5° from adirection that is parallel or perpendicular.

Elements which in their form or function are similar or close may bedenoted by identical references from one figure to another.

As FIGS. 1, 2A, 2B, 2C and 4 relate to one and the same embodiment, theywill be commented upon simultaneously.

FIG. 5 shows a depiction that is highly schematic, in order to make theinvention easier to understand, of an example of an injection deviceaccording to one embodiment of the invention. That figure is notstrictly in proportion.

With reference to this FIG. 5, an injection device 10, also referred toas an injector, comprises a body 300 the walls 301 of which define arecess 107 extending axially, along the axis (X). The body 300 may bemade in one or several parts.

A gas injection assembly 200 is mounted at one end of the body 300. Thisassembly defines a passage for the gas 202 from a gas inlet 105 open tothe outside and towards a gas outlet 203 opening onto the inside of therecess 107.

Liquid is introduced by a liquid inlet orifice 150 formed in a wall 301of the body so that the liquid introduced into the injector 10 has avelocity with a radial component. The liquid then flows along inside aspace 204 between the walls 301 and the gas injection assembly 200.

The walls define a constriction ending at a circular sharp-edged line131.

More specifically, the cross section of the cavity 107 upstream of thesharp-edged line 131 decreases as this line 131 is gradually neared. Thecross section of the cavity 107 downstream of the sharp-edged line 131increases with increasing distance away from this line 131.Alternatively, provision could be made for the cross section of thecavity 107 to remain constant downstream of the sharp-edged line, namelyfor the recess to comprise a portion defining a cylindrical duct, thesharp-edged line then constituting the base of this cylinder.

The stream of pressurized gas ejected at the gas outlet 203 reaches awall portion or zone 139 in close proximity to the sharp-edged line.Without wishing to be tied to a theory, it is possible that the liquidfilm passing near the sharp edge is sheared by the jet of gas, thuscausing the liquid to be atomized into droplets.

The injection assembly comprises a cylindrical tube 166 and a rodelement 168 housed inside this tube 166. The gas injected at the gasinlet 105 therefore circulates along a passage 202 of annular crosssection between two concentric walls.

In the embodiment depicted, the stream of pressurized gas ejected at thegas outlet 203 forms a thin layer of cylindrical shape.

In an alternative embodiment that has not been depicted, the injectionassembly could be configured so that the stream of gas is shaped as aportion of a cone.

This thin layer is centred on a wall portion in proximity to the sharpedge, for example in a zone including the sharp edge as in FIG. 5.

The stream of atomized liquid and of remaining gas are discharged via anorifice 18.

FIGS. 1, 2A, 2B, 2C and 4 relate to an embodiment of the invention thathas undergone testing.

An injection device 10 is intended to atomize a liquid into dropletsusing a gas. This injection device 10 comprises an end piece 118defining an outlet orifice 18 for discharging the atomized liquid andmounted on a body 300.

This body 300 extends axially along an axis (X) and has a cylindricalexterior shape over the majority of its length.

The body 300 defines a gas inlet orifice 105, at the opposite end to theoutlet orifice 18, and a liquid inlet orifice 150 formed in a lateralwall of the injection device 10.

The body 300 is made in several parts, namely:

-   -   a stopper 110 in which is defined a through duct through which        the gas entering the injection device 10 passes and which has        two flats 111,    -   a first gas feed element 106, comprising a base 165 and a        cylindrical tube 166, this base 165 and this tube 166 defining a        duct opening at each side of this element 106, the duct having        walls that are flared slightly at the base 165,    -   a second gas feed element 167, depicted on its own in FIG. 7 and        comprising a base 156 and a rod element, referred to as a        rod-shaped part 168, housed in the duct of the first gas feed        element 106,    -   a liquid feed element 120 in which the liquid inlet orifice 150        is defined; this element 120 is mounted on the stopper 110 and        defines a duct in which the first and second gas feed elements        106, 167 are housed,    -   a convergent nozzle 130 mounted on the liquid feed element 120        and on which the end piece 118 is mounted, this convergent        nozzle defining a duct that establishes fluidic communication        between the duct of the liquid feed element 120 and the outlet        orifice 18.

These various component parts 110, 106, 120, 130, 118 may be made ofsteel or the like, by machining or the like.

The base 156 of the second gas feed element 167 is held against thestopper 110 by the liquid feed element 120, and the base 165 of thefirst gas feed element 106 is held against the base 156 by this element120.

The base 156 defines a number of orifices 161, for example six orifices,which are arranged in such a way as to ensure fluidic communicationbetween the duct in the stopper 110 and the inside of the cylindricaltube 166.

The gas received at the gas inlet orifice 105 and that circulatesthrough these orifices 161 then enters a space 201 between the internalwalls of the duct in the base 165 and the external walls of the portionof the rod-shaped part 168 that is housed in this duct in the base 165,then into a space 202 between the internal walls of the cylindrical tube166 and the external walls of the portion of the rod-shaped part 168.The space 202 opens onto a gas outlet 203 of annular cross section.

The gas thus flows between two walls. The stream of gas has a relativelysmall cross section in these spaces 201, 202 so that the velocity of thegas at the gas outlet 203 is relatively high.

With reference in particular to FIG. 4, the rod-shaped part 168 is veryslightly flared over a portion 169′ so that the diameter of the crosssection of the rod increases very slightly, over this rod portion, witha gradual increase with distance away from the base 156, and is flared169 more markedly near the opposite end 170 to the base 156, still inthe direction of the diameter of the cross section increasing withincreasing distance away from the base 156.

Thus, the bore section 202 decreases near the gas outlet 203. The gasejected may thus have a particularly high velocity.

Because the flared portion 169 ends upstream of the gas outlet orifice203, the gas circulating throughout the gas injection assemblytherefore, immediately before being ejected via the gas outlet 203,passes through an annular zone of constant cross section (give or takethe precision of the machining) over a portion of the assembly 200, andof very small thickness, in this case comprised between 1 and 2millimetres thick.

Studs 210 keep the rod-shaped part 168 positioned centrally in thecylindrical tube 166.

The internal walls of the convergent nozzle 130 are configured to havean annular sharp edge 131. More specifically, the convergent nozzledefines a throttling portion 136 between a portion 133 configured tocollaborate with the liquid feed element 120, and a portion 134 thatdefines a cylindrical duct 135. The sharp edge 131 is located at themeeting point of the internal walls 132 of the throttling portion 136and the internal walls 137 of the cylindrical duct 135 of the portion134.

The internal walls 132 of the throttling portion 136 define a truncatedspherical surface.

The duct 135 opens onto a slightly flared duct 138. The walls of theduct 138 may define, with the walls of the duct 135, an angle of around3.5°. Without wishing to be tied to a theory, it is possible that thisvertex angle of the orifice of the convergent nozzle 130 makes itpossible to avoid boundary layer separation.

The liquid received at the inlet 150 flows along a space 204 between theinternal walls of the liquid feed element 120 and the external walls ofthe cylindrical tube 166.

The injection device 10 is arranged so that the gas outlet 203 faces thesharp edge 131 over the entirety of the line of this sharp edge 131 sothat the stream of gas at this gas outlet 203 is directed towards a wallportion in proximity to the sharp edge, for example exactly on the sharpedge or on the walls less than 1 centimetre away from the sharp edge,for example less than 1 millimetre away from the sharp edge.

Without wishing to be tied to a theory, it is possible that:

-   -   the liquid flowing through the space 204 is pressed firmly        against the walls of the spherical surface portion 132 by the        stream of air emanating from the gas outlet 203, this stream of        cylindrical shape acting like a thin layer of air preventing        fluid from passing towards the centre, or that this liquid is        pressed firmly against the walls as a result of the depression        in the space 204 which is created by the stream of air, and/or        that    -   the stream of gas reaching the internal walls in the vicinity of        the sharp-edged line 131, for example the end of the internal        walls 132 and/or the end of the internal walls of the portion        134, has a tendency to shear the film of liquid pressed firmly        against the internal walls in this zone, thereby creating        droplets of liquid and/or tends to impinge on the liquid with        enough kinetic energy that the energy associated with the        collision disperses the liquid into small-sized droplets.

The atomizing gas thus produced passes along the duct 135 and isdischarged by the orifice 18.

Alternatively, in an embodiment which has not been depicted, acountersink rather than a spherical surface 13 could have been planned.

It would appear to be advantageous to plan a surface shape upstream ofthe sharp edge that is such that the velocity of a fluid pressed firmlyagainst this surface has a component perpendicular to the direction offlow of the gas, in this instance the axial direction, that isrelatively high. The fact that the velocities of the liquid and of thegas are relatively perpendicular to one another could encourage shear atthe sharp corner and/or could encourage the formation of droplets as aresult of the conversion of the impact energy.

The internal dimensions of the injection device depicted in FIGS. 1, 2A,2B, 2C are similar to the dimensions habitually used for injectiondevices using a Venturi. By way of example:

-   -   The diameter of the gas inlet orifice 105 may be around 20        centimetres,    -   the bases 156 and 165 may have an outside diameter of around 25        centimetres,    -   the orifices 161 may have an inside diameter of around 2.2        centimetres,    -   the base 156 may have a thickness of around 4 centimetres,    -   the rod-shaped part 168 may have a length of around 77.4        centimetres and the cross section of this rod may have a        diameter varying between around 4.5 centimetres at the base 156        and around 7.15 centimetres at the end 170, the flare 169        corresponding to a variation in diameter from around 5.5        centimetres to this end value diameter of around 7.15        centimetres,    -   the cylindrical tube may have a length of around 69.4        centimetres, an outside diameter of around 9.5 centimetres and        may define a duct approximately 7.5 centimetres in diameter,    -   the base 165 may have a thickness (in the axial direction X) of        around 8 centimetres, and the diameter of the cross section of        the duct formed in this base may vary between around 9.22        centimetres and the diameter of the cylindrical tube 166, namely        around 7.5 centimetres,    -   the liquid feed element 120 may have an outside diameter of        around 50 centimetres and define a duct around 67 centimetres        long and around 16 centimetres in diameter,    -   the liquid inlet orifice 150 may have a diameter of around 14        centimetres and be positioned around 50-60 centimetres away from        that end of the element 120 that is intended to be in contact        with the convergent nozzle 130,    -   the portion 133 of the convergent nozzle may have a thickness        (in the axial direction X) of around 10 centimetres,    -   the throttling portion 136 of the convergent nozzle may have a        thickness (in the axial direction X) of around 6 centimetres,    -   the portion 134 of the convergent nozzle may define a        cylindrical duct 135 around 36 centimetres long and a slightly        flared duct 138 around 6 centimetres long, the diameter of the        duct 135 being around 7.3 centimetres and the diameter at the        outlet of the duct 138 being 8 centimetres.

The end of the injection device 10 via which the spray of atomizedliquid emerges is generally rounded, for example spherical. The outletorifice 18 in this end may have a shape similar to shapes of theconventional impact injection devices and may be chosen according to thedesired shape of spray. This may be a cylindrical, frustoconical,slotted or some other shape of orifice.

Example

An injection device similar to the one described with reference to FIGS.1, 2A, 2B, 2C and 4 was produced with dimensions one tenth of thedimensions described hereinabove.

The liquid chosen for such a test was water, the gas being air.

The injection device tested particularly has the following dimensions:

-   -   thickness (in a radial direction) of the space 204 of the liquid        flow path: between 3 and 3.5 millimetres for this 1/10^(th)        scale production, which would correspond to a thickness of 3-4        centimetres,    -   length of the liquid flow path between the inlet 150 and the end        of the cylindrical tube 166: between 50 and 60 millimetres,        which would correspond to a length of between 50 and 60        centimetres,    -   thickness (in a radial direction) of the space 204 of the gas        flow path prior to ejection via the outlet 203: between 1.5        millimetres at the base 165 and around 0.17 millimetres at the        outlet 203, still for this 1/10^(th) scale production,    -   diameter of the cylindrical duct 135 of the convergent nozzle;        7.30 millimetres, still for this 1/10^(th) scale production,    -   outlet orifice: slot 2.52 mm thick for this 1/10^(th) scale        prototype and with an angular aperture size of 105° (slot made        on a spherical end with an external radius of 5.6 mm for this        prototype).

For this 1/10^(th) scale production, the test conditions were asfollows:

-   -   Water flow rate: 226.2 kg/h,    -   Air flow rate: 9 kg/h,    -   Gas/liquid ratio: 4 wt %.

Measure of Pressure Drop

The injection device tested diffuses into the ambient air. Therefore theliquid pressure at the inlet is equal to the pressure drop. Thismeasurement was taken using a pressure gauge measuring the pressure atinlet.

The liquid pressure at the inlet was measured at 1.3 barg for theinjection device. The pressure drop is therefore relatively low.

Measuring the Droplet Size and Distribution Thereof

FIG. 3 is a graph with the abscissa axis denoting a value of measurementangle, with respect to the atomized liquid outlet orifice of theinjection device, without dimensions, and the ordinate axis depictingvalues, likewise dimensionless, of mean droplet size measured 30centimetres away from this orifice, for these angle values.

The curve 351 corresponds to the values obtained with a 1/10^(th) scaleprototype of a reference injection device with a Venturi.

The curve 352 corresponds to the values obtained with the 1/10^(th)scale prototype of the injection device of FIGS. 1, 2A, 2B and 2C.

As may be seen, using the prototype of the injection device of FIGS. 1,2A, 2B and 2C, the droplets have a mean diameter that varies relativelylittle with spray angle.

This mean diameter falls at around 100 microns.

To sum up, the injection device described hereinabove makes it possibleto obtain a spray of relatively fine droplets, with a relatively uniformdistribution, a considerably lower pressure drop, meaning that heavycharges can be treated without the need to use powerful pumps or anexcessive quantity of steam.

1. An injection device configured to atomize a liquid into dropletsusing a gas, comprising: a body comprising walls defining a recessextending axially so that said recess opens on the one hand towards agas inlet orifice at one end of the injection device and, on the otherhand, towards an atomized-liquid outlet orifice at the other end of saidinjection device, and a liquid inlet orifice being formed in said walls,said liquid inlet orifice extending along a radial component so as toopen, on the one hand, to the outside of the body and, on the otherhand, onto the recess, a gas injection assembly in which there isdefined a passage for the circulation of gas between the gas inletorifice and a gas outlet orifice situated inside the recess, wherein theinternal walls of the body define a constriction the throat of which isdownstream of the gas outlet orifice, the gas injection assemblydefines, with the walls, a space for the circulation of liquid from theliquid inlet orifice towards the throat of the constriction, and theinjection device is arranged in such a way that the stream of gasemanating from the gas outlet orifice in close proximity to the throatof the constriction.
 2. The injection device according to claim 1,wherein the gas outlet orifice is a slot facing the throat so that thestream of gas is circumscribed in close proximity to said throat.
 3. Theinjection device according to claim 2, wherein the throat and the slotof the gas outlet orifice have circular shapes.
 4. The injection deviceaccording to claim 2, wherein the gas injection assembly comprises atube and a rod element housed in said tube, said rod element extendinglongitudinally inside said tube so that the passage for the circulationof gas is between said rod element and said tube.
 5. The injectiondevice according to claim 4, wherein at least one of the rod element andthe tube is configured so that the thickness of the passage for thecirculation of gas undergoes throttling that accelerates the velocity ofthe gas between the gas inlet and the gas outlet.
 6. The injectiondevice according to claim 1 wherein the throat is a sharp-edged line. 7.The injection device according to claim 1, wherein the body defines acylindrical duct downstream of the throat.
 8. The injection deviceaccording to claim 7, wherein the cylindrical duct extends axially overa length of magnitude at least four times greater than the magnitude ofa diameter of the cross section of said duct.
 9. The injection deviceaccording to claim 1, wherein the recess is slightly flared downstreamof the constriction.
 10. A reactor for treating a charge ofhydrocarbons, notably for catalytic cracking, comprising at least oneinjection device according to claim 1 arranged in such a way that itsoutlet orifice for atomized liquid opens inside said reactor.
 11. Amethod for the catalytic cracking of a charge of hydrocarbons in areactor, in which method said charge of hydrocarbons is injected,preferably continuously, into said reactor, said charge of hydrocarbonsbeing injected via a liquid inlet duct connected to the liquid inletorifice of an injection device configured to atomize a liquid intodroplets using a gas, the injection device comprising: a body comprisingwalls defining a recess extending axially so that it opens on the onehand towards a gas inlet orifice at one end of the injection device and,on the other hand, towards an atomized-liquid outlet orifice at theother end of said injection device, and a liquid inlet orifice beingformed in said walls, said liquid inlet orifice extending along a radialcomponent so as to open, on the one hand, to the outside of the bodyand, on the other hand, onto the recess, a gas injection assembly inwhich there is defined a passage for the circulation of gas between thegas inlet orifice and a gas outlet orifice situated inside the recess,wherein the internal walls of the body define a constriction, the throatof which is downstream of the gas outlet orifice, the gas injectionassembly defines, with the walls, a space for the circulation of liquidfrom the liquid inlet orifice towards the throat of the constriction,and the injection device is arranged in such a way that the stream ofgas emanating from the gas outlet orifice covers a wall portion in closeproximity to the throat of the constriction; a gas being fed into saidinjection device via the gas inlet orifice.
 12. The catalytic crackingmethod according to claim 11, wherein the flow rates of hydrocarboncharge and of gas fed to the injection device are controlled in such away as to obtain a specific flow rate of hydrocarbons charge at thethroat of the injection device ranging from 1000 to 2000 kg/m²/s,preferably from 1400 to 1800 kg/m²/s.